Hallo, noble viewers, and welcome to Planet Earth: Our Loving Home. Today we’ll explore the phenomenon of mass extinction, by which large numbers of species cease to exist.

Scientists say that many such events have occurred over the course of Earth’s history, and with the acceleration of global warming they warn that our planet may be headed toward another one.

Today Dr. Peter Ward, a professor of Earth and Space Sciences at the University of Washington in Seattle, USA and an astrobiologist for the National Aeronautics and Space Administration (NASA) will share his knowledge.

Dr. Ward is an expert in the area of mass extinction and has written more than a dozen books, including the critically acclaimed “Under a Green Sky: Global Warming, the Mass Extinctions of the Past and What They Can Tell Us About Our Future.”

Prof. Ward: What has caused mass extinctions is still one of the really interesting and driving questions in geology and biology. If you would have asked me that question between 1980 and 1990, I would have told you that asteroid or comet impact on the planet would have been the major or perhaps the only cause of past mass extinctions.

It really now looks like that was a unique event, and that the other 14 mass extinctions were caused by short-term climate change, in almost every case global warming.

HOST: According to Dr. Ward, changes to the composition of the ocean can initiate a mass extinction.

Prof. Ward: The ocean state that we have now is one where our oceans are mixed,and that means that the composition of water, the chemistry of sea water at the top is almost identical to that at the bottom.

And by chemistry I don’t just mean the atoms making up the water, I mean the entire body of water itself, which includes dissolved gasses. Now gas in this atmosphere, if we bring out a new vat of seawater that’s been out of gas, that gas sitting here will pull down molecules of oxygen, carbon dioxide, nitrogen and it will dissolve away; just like you put sugar to water and stir it, well, gas does the same thing.

The amount of oxygen at the surface of the ocean is almost identical to the amount at the deep bottom, that’s the current ocean state. But the second ocean state is there is oxygen at the top, but none on the bottom. The third ocean state, there is not much oxygen anywhere, and hydrogen sulfide is present; three ocean states.

Prof. Ward(m): The mass extinctions happen when you move to either of the other ones.